Lab Evaluation and Comparison of Corrosion Performance of Mg Alloys 2010-01-0728

More Mg alloys are being considered for uses in the automotive industry. Since the corrosion performance of Mg alloy components in practical service environments is unknown, long term corrosion testing at automotive proving grounds will be an essential step before Mg alloy components can be implemented in vehicles. However, testing so many Mg alloy candidates for various parts is labor intensive for the corrosion engineers at the proving grounds. This report presents preliminary results in evaluating corrosion performance of Mg alloys based on rapid corrosion and electrochemical tests in the lab. In this study, four Mg alloy candidates for transmission cases and oil pans: AE44, AXJ530, MRI153M and MRI230D were tested in the lab and at General Motors Corporation Milford Proving Ground and their corrosion results were compared. It was found that the general corrosion performance of the alloys as measured in the lab can be ranked in the following order: MRI230D≥MRI153M≻AE44≥AXJ530, which is consistent with the long term corrosion testing results measured via the GMW14872 test. The ranking obtained in this study can be used as a criterion in selecting alloys for Mg transmission case and oil pan applications. The study also suggests that the laboratory-based corrosion and electrochemical techniques can serve as preliminary corrosion evaluation tools in comparing the corrosion performance of various Mg alloys. After the lab evaluation, many unsuitable Mg alloys components or parts can be eliminated and thereby avoid the need for long term corrosion tests.